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    <script>
        let arr = [1,2,3,4,5,6,7];
        let nArr = []
        //从数组的长度递减 再将数组里面的值赋给新数组
        for(var i = arr.length -1; i>=0; i--){
             nArr[nArr.length] = arr[i];
        }
        console.log(nArr);
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